OTRC: Matthew McConaughey explains his newly scrawny appearance

Matthew McConaughey has explained that his newly gaunt look is for his upcoming role as an HIV positive patient in "The Dallas Buyer's Club."

"I'm playing a guy who was sick and would have loved to have been healthier but wasn't. For me, it's more of a mental thing than a physical thing," McConaughey told Us Weekly at the NYLON Guys and Macy's INC party in Santa Monica, Calif. on August 15. "I'll get down to the weight I need to get to. I'm on my way, and it's what I need to do for the job."

The 42-year-old actor told the weekly magazine that he has been eating "five ounces" of high-protein, low-carbohydrate foods to lose weight. He said that the small portion size was the hardest part of his new diet and he is looking forward to a eating a cheeseburger after he finishes the film.

McConaughey has also limited his physical activity mostly to cardio with "very, very little resistance."

"The Dallas Buyer's Club," follows electrician Ron Woodroof who develops full-blown AIDS in 1986 and after being told to "go home and die," sought underground pharmacies selling HIV drugs not approved in the U.S. His efforts eventually prolonged the lives of thousands of people and himself.

The film also stars Hilary Swank and is slated be directed by Jean-Marc Vallee, who helmed the Oscar-winning 2009 film, "The Young Victoria."

McConaughey helped to finance "The Dallas Buyer's Club." The film has had several false starts and the role of Ron Woodroof was nearly portrayed by Brad Pitt or Ryan Gosling.

McConaughey recently portrayed the owner and patriarch of an all-male strip club in the movie "Magic Mike." The actor is known for roles in films like "Dazed and Confused," "A Time to Kill," "How To Lose a Guy In 10 Days," and "The Lincoln Lawyer."

The pair has two children - 4-year-old son Levi and 2-year-old daughter Vida. The couple announced on July 4 that they were expecting a third child.

McConaughey told Us Weekly that in order to help out his pregnant wife, he has taken over some of the cooking responsibility.

"There's a Brazilian dish that her mother does, so we're having it more often than we're used to. That involves a lot of chicken, a lot of cheese and things like that, which I'm not having, but she is," McConaughey said. "She loves a good steak, so I've been making a good rib-eye for her when I can."